Method for controlling and/or monitoring a communication transmission equipment for transmission errors for the implementation of the method

ABSTRACT

In a method for controlling and/or monitoring wherein a polling unit (7, 8) exchanges information with processor units (6) in a callin mode, the processor units (6) can be switched from a first to a second transmission mode. In the first transmission mode, the telegrams are through-connected without intermediate storage; in the second transmission mode, they are through-connected only given freedom from error. The method can be advantageously employed in equipment for in-service monitoring of equipment of communication transmission technology.

BACKGROUND OF THE INVENTION

The invention is directed to a method for controlling and/or monitoringwhereby at lest one monitoring unit exchanges information with processorunits that are connected to the monitoring unit via a common telegramtransmission network and are provided with addresses and whereby pollingtelegrams of the monitoring unit and reply telegrams of the processorunits are transmitted.

Such a method is already disclosed by German Published Application 34 36414. In the known method, the addresses are set with the assistance ofcoding switches.

A method for in-service monitoring of a communication transmissionequipment wherein useful signals are transmitted via an electroopticaltransmission link and telemetry signals are transmitted via an auxiliarychannel is already known from Ewald Braun and Erhard Steiner:"Supervision and Additional Services for Digital Fiber-OpticTransmission Systems" telcom report 10 (1987) Special "Multiplexing andLine Transmission", pages 107 through 112.

The known method uses address-free telemetry telegrams, so that theprocessor units provided in the line terminal equipment and intermediaterepeaters of a transmission section need not be addressed. The method,however, can not be employed without further ado in communicationtransmission equipment that have a star or, respectively, treestructure. When processor units that are called under address control bya locating unit in cyclical succession are provided in the appertainingtelemetry means in a communication transmission network having star or,respectively, tree structure, then a structure corresponding to theuseful signal network can also be provided for the telegram transmissionnetwork of the telemetry means.

This is also true of equipment for distributing electrical energy or thelike that are to be monitored with the assistance of a remote controlmeans.

SUMMARY OF THE INVENTION

It is an object of the invention to specify a method and a circuitarrangement for the implementation of the method that allowdisadvantageous effects of disturbances in the telegram transmissionnetwork to be kept as small as possible. In particular, it shouldthereby be possible to localize the location of, in particular,brief-duration disturbances. The method and the circuit arrangementshould be preferably suitable for an especially reliable in-servicemonitoring of communication, preferably digital signal transmissionlinks.

For achieving this object, the method of the invention provides themethod steps as follows: for at least one part of the processor units,telegrams of at least one transmission direction are conducted via atransmission unit that through-connects the telegrams withoutintermediate storage in a first transmission mode and, in a secondtransmission mode, forwards the telegram after intermediate storage andchecking only when it is found that given demands are satisfied; and arespective switch from the first to the second transmission mode isundertaken as soon as the check in the appertaining processor unit findsthat a through-connected telegram does not satisfy the given demands.

The method of the invention allows a repeated forwarding of disturbedtelegrams to be prevented without the cycle time during normal operationbeing lengthened.

Advantageous developments of the method as well as expedient circuitarrangements for the implementation of the method are as follows:

The switching of the processor units form the second into the firsttransmission mod is respectively initiated by a control instruction ofthe monitoring unit. The processor units that have switched into thesecond transmission mode report the new mode in the reply telegramfollowing the switching and report the appertaining transmissiondirection to the monitoring unit.

The monitoring unit, following a message that a processor unit hasswitched into the second transmission mode, cyclically calls theprocessor units beginning with the processor unit that lies closest tothe monitoring unit and thereby respectively switches the processor unitand thereby respectively switches the processor units that are in thesecond transmission mode form the second transmission mode into thefirst transmission mode. The monitoring unit, as an error locating meansand/or in-service monitoring means, exchanges information with processorunits that are allocated to local ends or intermediate locations of acommunication transmission equipment.

A circuit arrangement for controlling and/or monitoring, comprising atleast one monitoring unit and comprising processor units that areconnected to the monitoring unit via a common telegram transmissionnetwork and provided with addresses, whereby the monitoring unitcomprises a means for transmitting polling telegrams and the processorunits each respectively comprise a means for transmitting replytelegrams, has the following components: for at least one transmissiondirection, at least one part of the processor units respectivelycontains transmission equipment having a switch-over means and containsan evaluation means provided with an intermediate memory for evaluatingreceived telegrams; and the switchover means is respectivelycontrollable by the evaluation means such that the output of theswitch-over means is connected via the switch-over means to the input ofthe transmission unit in a first transmission mode and is connected toan output of the intermediate memory in a second transmission mode. Thecontrol input of the switch-over means is connected to a control outputof the evaluation means that, when it is found that the prescribeddemands are not satisfied, outputs a first controls signal of the secondtransmission mode and, given reception of a telegram of the monitoringunit that contains a switch-back instruction, outputs a second controlsignal for the first transmission mode.

The circuit arrangement is fashioned as an error locating means and/orin-service monitoring means for transmission links of communicationtransmission technology having at least one transmission sectionrespectively arranged between two line terminal equipment and maypotentially contain one or more intermediate locations. The monitoringunit is formed by the error locating means and/or in-service monitoringmeans and the processor units are allocated to at least one part of theline terminal equipment and/or to at least one part of the intermediatelocations. The evaluation means can contain a microprocessor having aRAM as data store.

In the method, the query telegrams and reply telegrams, in particular,alternate with one another. Switching from the second transmission modeinto the first transmission mode can be automatically triggered after aprescribed time or at every other correct call.

In the method, the change-over can respectively ensue on the basis of acontrol instruction or on the basis of telegrams in and of themselves.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall be set forth in greater detail with reference to theexemplary embodiments shown in the figures.

The figures show equipment for in-service monitoring of communicationtransmission equipment, namely

FIG. 1 having a fundamental digital signal line section;

FIG. 2 having a line network composed of three fundamental digitalsignal line sections;

FIG. 3 having a star network containing a plurality of parallel lines;

FIG. 4 having a branch star network.

Further shown are:

FIG. 5 a block circuit diagram of a processor unit having a busterminal;

FIG. 6 a processor unit constructed in conformity with FIG. 5 butwithout a bus terminal.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Line terminal equipment, intermediate repeaters and light waveguides arethe basic elements of the digital signal transmission link shown in FIG.1 whose functionability and transmission properties are to be monitoredwith the assistance of devices of an equipment for in-service monitoringcomposed of the locating module 7, the personal computer 8 and thein-service monitoring processor units referred to below as processorunits 6.

The locating module can be omitted when the processor units 6 areexecuted such that they can be connected as master or as slave. Oneprocessor unit 6 must then be connected as master and assume the jobs ofthe locating module and the other processor units must be designed asslaves.

The smallest unit of a digital signal transmission link is a fundamentaldigital signal line section, referred to below as line section 4. In thetransmission equipment of FIG. 1, the line section is composed of twoline terminal equipment 1 and of one or more intermediate repeaters 2inserted into the link as needed.

A processor unit 6 that respectively receives the monitoring data fromthe main system to be monitored via an internal bus is inserted intoevery line terminal equipment 1 and into every intermediate repeater 2.

Dependent on the demands, the locating domain can be composed of thefollowing structures:

of a line that, conforming to FIG. 1 or, respectively, FIG. 2, iscomposed of one or more line sections connected in chain;

conforming to FIG. 3, of a network having a plurality of parallel lines;

conforming to FIG. 4, of a star network provided with branchings.

Dependent upon the application, the terminal K3a having twounidirectional interfaces or the terminal K3 having one bidirectionalinterface is employed.

The data of the processor units 6 are respectively coupled out within aline section 4 via the terminals K1, K2 and are transmitted in anauxiliary channel that is preferably superimposed on the useful signal.

Within a line, the data of the processor units 6 are coupled in and outof the auxiliary channel from line terminal equipment 1 to line terminalequipment 1 via the four-wire terminals K1, K2 and maybe transmittedfrom a line section 4a to the next line section 4b via the terminals K3or, respectfully, K3a.

In the arrangements shown in FIG. 2, the line sections 4a . . . 4c areconnected chained. The locating module 7 is connected to the processorunit 6 of the line terminal equipment 1 in one of the two local ends ofthe chain circuit. A personal computer 8 is connected to this locatingmodule 7. Further personal computers 8 are directly connected to theprocessor unit 6 of the first line terminal equipment 1 and to two ofthe intermediate repeaters 2n.

Useful signals are transmitted from line terminal equipment 1 to lineterminal equipment 1 within the line sections 4a . . . 4c. The data ofthe processor units 6 are transmitted within the line sections 4a . . .4c via a respective auxiliary channel and are transmitted between theline sections 4a . . . 4c via a respective ISM bus (in-servicemonitoring bus) 9 having the interface RS 485 (terminal K3 of theprocessor unit).

All processor units 6 additional have a terminal 90, particularly havingthe interface RS 232 C, to which a personal computer 8 can be connected.This possibility has been utilized at a line terminal equipment and attwo intermediate repeaters.

FIG. 3 shows two of a plurality of lines ending at the network node N(branching).

The processor units of the line terminal equipment 1 and the locatingmodule 7 are connected to one another via the ISM bus 9 at the networknode N.

According to FIG. 4, the locations A through G are connected to oneanother via a branched star network. A line section 4AB withoutintermediate repeater is provided between the locations A and B, twoline sections 4BC1, 4BC2 each having an intermediate repeater 2 areprovided between the locations B and C; a line section 4BD is providedbetween the location B and the location D; and a respective line section4DF and 4GE is provided between the location D and F and the location Dand G. The location E is also connected via a line section 4E to theintermediate repeater 2 of the line section 4BC2.

A respective personal computer 8 is connected to the processor unit ofthe line terminal equipment 1 at the locations A and C. The personalcomputer 8 can thereby optionally ensue [sic] at the ISM bus 9 with theinterface RS 485 or at an additional terminal of the processor unithaving the interface RS 232 C. In addition to the line terminalequipment 1 of the line sections ending thereat, the locating module 7is additionally connected to the ISM bus 9 at the location D, thislocating module 7 being provided with a means for polling control. Thelocating module 7 has an additional terminal 70 for the connection of asignal collecting means via which the monitoring data of the starnetwork can be called from the locating module 7 by the signalcollecting means.

Given a branch, the data of the processor units 6 are transmittedbetween the line terminal equipment 1 via the terminals K3 or,respectively, K3a and via a network node.

In the networks of FIGS. 1 through 4, a means for executive sequencing,particularly a locating module 7 and/or a personal computer 8 isconnected to one of the network nodes or to one of the processor units.The locating module 7 or a personal computer 8 successively polls theindividual processor units 6 via call-in telegram with their addresses,receives their monitoring data by reply telegram and evaluates thelatter.

In the method for in-service monitoring on which the followingdescription is based, the locating telegrams are asynchronouslytransmitted with a standard protocol conforming to IEC TC57. Otherprotocols such as CCITT X25 (HDLC) are also possible for thetransmission. In the master function, the locating module interrogatesthe processor units of the entire network.

During normal operation, i.e. in the fault free condition, all telegramsin the individual equipment formed by line terminal equipment andintermediate repeaters are connected through from the input to theoutput without intermediate storing. A short query cycle for anextensive network is thus achieved. In each processor unit provided forthe in-service monitoring in each and every line terminal equipment or,respectfully, intermediate repeater, the traversing telegrams, however,are investigated for errors and disturbances of the regular execution onthe basis of monitoring. When a faulty telegram is recognized by theprocessor unit of a line terminal equipment or, respectively,intermediate repeater, then the processor of this equipment switchesinto protected mode for the appertaining direction after the end of thistelegram.

A first modification of the method has the following execution:

Since no regeneration of the telegrams ensues, the error also occurs atall following devices. These thus likewise switch into protected mode.This means that all incoming telegrams are intermediately stored in theprocessor units from the first, disturbed regeneration section on, areinvestigated for errors and only error-free telegrams arethrough-connected to the output.

The following can thereby serve as error criteria:

parity via a character

check sum via the user data

matching of the two length particulars in the L-fields

matching of the length particular with the actual length

correct start and stop character

permanent transmission of formerly correct telegrams by a faultytransmitter

generating a break condition (continuous low) on the in-servicemonitoring channel

checking with cyclical protection code (cyclic redundancy check).

Every line terminal equipment or, respectively, every intermediaterepeater that has switched into the protected mode sends a telegram inboth directions that contains the identifier "protected mode". When adevice is already in protected mode when it receives this telegram andwhen it has already transmitted its telegram that indicates switchinginto the protected mode, then it does not forward the incoming telegram.

The master, particularly a locating module, immediately switches to thesearch-callin cycle after receiving a telegram having the identifier"protected mode". In this operating mode, the master--when the devicewas situated in the protected mode successively calls the equipment(line terminal equipment or, respectfully, intermediate repeaters)proceeding from the locating module and deprotects them. In their replytelegrams, the individual equipment tell whether they were in theprotected mode.

Two cases can be distinguished for identifying the error location.

When, beginning at the locating module up to a defined point of thelink, all devices were in the protected mode, then the location of theerror lies in the regeneration section following the device that was thelast that was in the protected mode. An error is thus present in thereturn direction of the link.

When, beginning at the locating module, devices are in protected modeonly after a certain point of the link, then the error location lies inthe regeneration section preceding the device that was the first to bein protected mode. An error is thus present in the forward direction ofthe link.

The search-callin cycle is executed with the same speed as the ordinarycallin cycle since the addressed devices are respectively deprotectedbeginning with the first device following the locating module and, thus,the intermediate storage of the telegrams is again eliminated. Acritical advantage of the method lies therein that only correcttelegrams are forwarded in the operating mode of "protected mode". Datacollision, ambiguous or garbled telegrams can thus not occur even in theerror case.

In a second modification of the method, the locating module 7--in theprotected mode--successively calls the individual line terminalequipment and intermediate repeaters 2 in with their address (calltelegram) and subsequently receives a reply telegram with the ISM(in-service monitoring) message contents.

In the error-free condition, all callin and reply telegrams arriving ata line terminal equipment or, respectively, intermediate repeater arethrough-connected to the output without intermediate storage in order tokeep the time of a polling cycle as short as possible. The traversingtelegrams, however, are monitored for errors and disturbances of theregular execution in the processor unit 6 of each and every lineterminal equipment 1 or, respectively, intermediate repeater 2. When theprocessor unit 6 of a line terminal equipment 1 or, respectively,intermediate repeater 2 subsequently recognizes an error in one of thetraversing telegrams, then the processor unit of this device as well asall processor units in the following devices switch into thetransmission mode of "protected mode" for this direction. Beginning withthe first disturbed regeneration section, this means that all incomingtelegrams in this transmission direction are intermediately stored inthe processor units, are checked for errors and that only error-freetelegrams are through connected to the respective output.

The following, for example, are the error criteria:

parity and block check must be correct;

length of the telegram must match with the length particular in theL-field of the telegram header.

The transmission mode of "protected mode" can be activated anddeactivated in every equipment on the basis of a control instructionfrom the locating module/personal computer.

The transmission mode of "protected mode" and the transmission directionpertaining thereto are reported to the polling locating module/personalcomputer in the reply telegram.

Due to the intermediate storage of the telegrams in the processor unitsof each and every line terminal equipment/intermediate repeater that isneeded in the protected mode, a polling cycle in this mode lastssignificantly longer than during normal operation.

The following execution is proposed in order to keep the time for apolling cycle optimally short even given disturbances:

After receiving the information that an equipment has switched into the"protected mode", the locating module immediately starts a new pollingcycle. In this polling cycle, the locating module begins with the callinof the equipment that lies closest to it and, with a controlinstruction, switches this equipment back into the normal mode.Subsequently, the equipment lying therebehind is called and is likewiseswitched into normal operation. This procedure is continued until thelast equipment of a line has been called in. What is achieved in thisway is that--given callin of an equipment--all equipment lying betweenthe locating module and the called equipment are switched into normaloperation. The polling cycle with switching into normal operation thuslasts no longer than a polling cycle with equipment that are in normaloperation.

Since, given a disturbance, all devices following the location of thedisturbance (in transmission direction) switch into the "protectedmode", the location of the disturbance can also be unambiguouslyidentified.

Sporadically occurring errors in the ISM channel can therefore also bereliably located with this method.

When a call telegram is disturbed and, as a result thereof, does notcontain the given instructions, no processor unit assembly sends a replytelegram. Given permanent faults, only the processor unit situated infront of the fault location send a reply telegram.

When a reply telegram is disturbed and therefore does not contain thegiven instructions, this is recognized by the locating module/personalcomputer. Given permanent faults, the locating module/personal computerreceives correct reply telegrams only from processor units that aresituated in front of the location of the fault.

The location of the fault can therefore also be identified givenpermanent faults.

The processor unit can be switched between two modes for thetransmission of the telegrams.

1. Normal mode: All telegrams incoming at the interfaces are immediatelyforwarded to the next line equipment and, in parallel thereto, arechecked by the microprocessor for their content.

2. Protected mode: All telegrams incoming at the interfaces are firstchecked by the microprocessor for their content before they areforwarded to the next line equipment.

The processor unit shown in FIG. 5 has an input E1 and output Al for theconnection of a first four-wire data channel for the transmission oftelegrams, has an input E2 and output A2 for the connection of a secondfour-wire data channel and has a third input E3 and output A3 for theconnection of a third four-wire data channel.

Each of three outputs Al, A2 and A3 can be optionally connected to theoutput of an exclusive-OR element 37, 30 or, respectively, 12 or to theoutput of a parallel-to-serial converter 23, being connectable theretovia a switch-over means 36, 31 or, respectively, 13 that is controllableby the microprocessor 35. This parallel-to-serial converter 23 has itsparallel input connected to the port PO of the microprocessor 35. Theswitch-over means 36 is thereby controlled via the two-lead control lineSt5, the switch-over means 13 is controlled via the two-lead controlline St3 and the switch-over means 31 is controlled via the two-leadcontrol line St6, being all controlled by the microprocessor 35.

The exclusive-OR elements 12, 30 and 37 that respectively lead to anoutput of one of the three four-wire terminals operate the data incomingat the inputs of the two other four-wire terminals.

The serial-to-parallel converts 20, 22, 24 and 25 as well as theparallel-to-serial converters 21 and 23 are contained in UART modules orin HDLC modules. The serial-to-parallel or, respectively,parallel-to-serial converters 20 through 25 are connected via an 8-bitparallel bus to the port PO of the microprocessor 35 and are selected bythe chip select module 26 connected to the microprocessor 35. On thebasis of the interrupt module 27 that is likewise connected to themicroprocessor 35, they interrupt the program of the microprocessor asneeded.

The coding switch 29 with whose assistance the processor unit can be setto an address is also connected to the port PO of the microprocessor 35via the switch 28.

The RAM 32 serving as data store, the EPROM 33 serving as programmemory, the EEPROM 34 serving as non-volatile data store and the module38 for self-monitoring are also connected to the microprocessor 35.

The output of the exclusive-OR element 12 is conducted to the one inputof the OR element 15 via the means 14a for signal edge recognition andvia the means 14b connected in chain therewith. Together with a controlinput of the means 14a and 14b, the other input of the OR element 15 isconnected to the control line St2 coming from the microprocessor 35. Thetransmission-reception module 11 lies between the four-wire terminalpair E3, A3 and the bus terminal K3 for the connection of abidirectional bus. The control input of this transmission and receptionmodule 11 via which the transmitter D or the receiver R can beoptionally activated is connected to the output of the OR element 15.

During normal operation, the telegrams are directly forwarded from thedata input E1 or E3 to the output A2 via the exclusive-OR element 30 andvia the switch 31. From input E2 or E3, the telegrams proceed to theoutput Al via the exclusive-OR element 37 and via the switch 36.

The exclusive-OR element 12 or, respectively, 30 or, respectively, 37sees to it that no data are transmitted when data simultaneously arriveat the inputs E1 and E2 or, respectively, E1 and E3 or, respectively, E2and E3.

Since no data dare arrive simultaneously at the input E1, E2 and E3given error-free operation, the exclusive-OR elements 12, 37 and 30inhibit data only in case of error.

Data that arrive at the input E1 or E2 can also proceed via theexclusive-OR element 12 and the switch 13 to the transmitter D of thetransmission-reception module 11 and can proceed from the latter to thebus terminal K3. To this end, the switch 13 must be situated in theillustrated, normal position and the transmitter D must be activated.This is the case when the means 14a recognizes a leading edge and the ORelement 15 receives a corresponding control potential via the means 14band/or via the control line St2.

When, during normal operation, data are conducted via the exclusive-ORelement 12 to the bus terminal K3, then these data are also suppliedinto the means 14a for signal edge recognition. When the means 14a forsignal edge recognition recognizes the leading edge of the first bit ofa telegram, then it starts the timer circuit 14b. This timer circuitoutputs an output pulse that is independent of the bit sequence thatarrives at the input of the means 14a for signal edge recognition. Theoutput pulse proceeds via the OR element 15 to thetransmission-reception module 11 and, thereat, immediately engages thedriver module D and disengages the reception module R. Data that arriveat one of the inputs E1 or E2 of the processor unit are thus immediatelyforwarded to the bus terminal K3 by the recognition of a leading edge.

Simultaneously, the data are transmitted to the microprocessor 35 forprocessing. Data that arrive at the input E1 proceed to themicroprocessor 35 via the serial-to-parallel converter 22; data from theinput E2 proceed to the microprocessor 35 via the serial-to-parallel 25;and data from the input E3 proceed to the microprocessor 35 via theserial-to-parallel converter 24. The serial-to-parallel converters 22,24 and 25 accept the data byte-by-byte and always output an interruptpulse to the microprocessor 35 whenever they have loaded a byte in orderto output it to the port PO of the microprocessor 35. When themicroprocessor 35 finds that the data satisfy given demands, then itactivates the control line St2. As a result thereof, the microprocessor35 activates the driver module D of the interface module 11 via the ORelement 15.

When, while evaluating a telegram, the microprocessor 35 finds thatgiven demands were not satisfied, then it initiates the processor unitto switch into a protected mode. In the protected mode, themicroprocessor 35 activates two of the three control lines St3, St5 andSt6. Two of the three switches 13, 31 and 36 are therefore switched, sothat all data that the parallel-to-serial converter 23 outputs proceedto two of the three outputs A1, A2, K3 from whose direction the telegramwas not received.

The data incoming at the input E1 are processed in theserial-to-parallel converter 21; the data incoming at the input E2 areprocessed in the serial-to-parallel converter 25. The microprocessorthus recognizes the direction from which the data comes. In theprotected mode, the control lines St6 and the control lines St5 aretherefore activated such that the output A1 or A2 via which transmissionis not carried out is applied to high potential via the switches 31 or36 and via the pull-up resistor.

The signal collector 18 is connected to the microprocessor 35 via theinterface module 19 and via the serial-to-parallel converter 20 and theparallel-to-serial converter 21. The signal collector 18 supplies themonitoring data of the monitored intermediate location and, aswarranted, receives the control information contained in the callintelegram for forwarding to a signal collecting means (not shown). Theprocessor 35 transmits the monitoring data of the monitored intermediatelocation in all three directions K1, K2 and K3 via the switch-over means13, 31, 36 and via the outputs A1, A2, A3. When a plurality of terminalsK3 are connected to one another via a bidirectional bus at a networknode, then the following sequence derives for the engagement anddisengagement of a bus driver:

In the quiescent condition, all drivers are inactive and have ahigh-impedance output. When data arrive at the terminal K1 or K2, thetimer 14b is started by the signal edge of the start bit, this timer 14bactivating the driver for at least two characters. The further holdingand deactivation is then assumed by the microcomputer 35 to which thedata were supplied parallel.

The invention is not limited to the particular details of the method andapparatus depicted and other modifications and applications arecontemplated. Certain other changes may be made in the above describedmethod and apparatus without departing from the true spirit and scope ofthe invention herein involved. It is intended, therefore, that thesubject matter in the above depiction shall be interpreted asillustrative and not in a limiting sense.

We claim:
 1. A method for controlling and/or monitoring, whereby atleast one monitoring unit exchanges information with processor unitsthat are connected to the monitoring unit via a common telegramtransmission network and are provided with addresses, whereby pollingtelegrams of the monitoring unit and reply telegrams of the processorunits are transmitted, comprising the steps of:for at least one of theprocessor units; receiving a telegram in at lest one transmissiondirection; in a first transmission mode, of the associated processorunit, sending the telegram without intermediate storage; in a secondtransmission mode of the associated processor unit, intermediatelystoring the telegram, check the telegram for errors and sending thetelegram only if no errors are identified in the telegram; andimmediately switching the associated processor unit from the firsttransmission mode to the second transmission mode when errors areidentified in the telegrams as a result of checking he telegram forerrors during the first transmission mode.
 2. The method according toclaim 1, wherein switching of the processor units from the secondtransmission mode to the first transmission mode is respectivelyinitiated by a control instruction of the monitoring unit.
 3. The methodaccording to claim 1, wherein the processor units that have switchedinto the second transmission mode report the new mode in the replytelegram following the switching and report the appertainingtransmission direction to the monitoring unit.
 4. The method accordingto claim 3, wherein the monitoring unit, following a message that aprocessor unit has switched into the second transmission mode,cyclically calls the processor units beginning with the processor unitthat lies closest to the monitoring unit and sends a control instructionthat switches the processor units that are in the second transmissionmode from the second transmission mode into the first transmission mode.5. The method according to claim 1, wherein the monitoring unit is as anerror locating means and exchanges information with processor units thatare allocated to locations of a communication transmission equipment. 6.The method according to claim 1, wherein the monitoring unit is anin-service monitoring means and exchanges information with processorunits that are allocated to locations of a communication transmissionequipment.